1. Field of the Invention
The present invention relates to a system for purifying liquid, and in particular water, by oxidizing contaminants in the liquid.
2. Description of the Related Art
There is an ever increasing need for purifying liquids, and in particular water. There are a number of applications where water needs to be purified and decontaminated, and a few of these are swimming pools and recreational baths, green houses, animal farms, cooling towers, hospitals etc. The conventional technologies for purifying and decontaminating water for most applications include the use of chemicals that are mixed with the water. Due to environmental aspects and the impact that chemicals have on the environment, humans and animals, there is a strive to reduce the use of chemicals.
One approach to purify/decontaminate water has been to use ozone. Several methods have been developed in several countries for purifying water with ozone (O3) in drinking water installations and bathing facilities, and also ozone dissolved in water for cleaning, disinfection and sterilization of articles. A combination of ozone, oxygen, hydrogen peroxide and UV radiation means that the reaction proceeds much more quickly and more efficiently by virtue of the generation of more free radicals.
The inactivation of microorganisms with the aid of ozone and radicals is considered as an oxidation reaction. The membrane of the micro-organism is the first to be attacked. Within the membrane/cell wall, the ozone and the radicals destroy nuclear material inside the cell/virus/spore. The inactivation reaction in the case of most micro-organisms occurs within minutes, depending on the ozone dose and the amount of free radicals which are formed.
Despite its solubility in cold water, ozone is broken down (=consumed) quickly, as is the case in air, which gives a great many different radicals and more or less stable by-products such as aldehydes, bromate and carboxylic acids. The degree of breaking down depends on the pH, the substance which is exposed and the temperature. Certain substances are broken down easily by the ozone. However, the majority of substances and molecules are oxidized more efficiently by free radicals which are formed by ozone and the media treated by ozone.
One very efficient method of using free radicals in the oxidizing process is disclosed in the international patent application No. WO 96/20017. The method utilises UV-radiation to create ozone in air and liquid, radiates the ozone with certain wave-lengths in order to obtain free radicals, which oxidize the contaminants in the air or liquid. In order to increase the production of free radicals, catalysts are used, for example titanium oxides. The applicant of the above patent application has obtained very good results in purifying/decontaminating water in cooling towers, swimming pools, green houses, to name a few applications. The use of the patented method has enabled a complete removal of chemicals in those applications.
However, for certain applications, the device for purifying water or other liquids described in WO 96/20017 has capacity limitations as regards the amount to be treated per time period. Trials have been made to reduce the flow past the UV-radiation sources, to use the device also during periods when no consumption of water is taking place and to store the purified water in intermediate tanks. This has the drawback that additional space has to be available in order to accommodate the intermediate tanks. For some applications this might not be feasible and for some applications and large consumers it is not an optimal solution. There has also been a need from customers to be able to arrange the device so that minimal floor space is occupied.
Another application with specific problems is found in water systems in building. This is in connection with legionella bacteria, a water-based organism which causes infection when inhaled in an aerosol form, which is a huge problem all over the world, and is especially troublesome in hospitals, if already weak and sick people receive the bacteria via for example showers. If the tap-water is not hot enough the bacteria may thrive and multiply uncontrolled. The main solution to this problem has been to increase and to try to control the temperature of the water in order to prevent the occurrence of legionella bacteria. Chemicals that are able to kill these bacteria cannot usually be used for these applications since they may be harmful also to humans.
For certain applications, the above mentioned method has some shortcomings. If the liquid is heavily contaminated, the amount of ozone might not be sufficient to generate the amount of radicals needed for a complete removal of contaminants in the liquid. This may be due to that the radiating energy for creating ozone in the liquid either is absorbed or blocked by the contaminants or other particles/matter in the liquid. In for example treatment of salt water a lot of energy is absorbed by halogens. Thereby not enough ozone is created and thus not enough radicals for the purification process. There might also be the case that the amount of oxygen for creating ozone is insufficient.
In view of the above it would therefore be advantageous to increase the ozone content in a simple and economical way using the radicals as the primary purification oxidants. Regarding the application treating salt or brackish water it would be advantageous to use a continuous system.
There is thus a need for improvements in this technical area.